1. Field of the Invention
The present invention relates to circuits and methodology to provide redundancy in a switching power system. More particularly, the present invention provides a redundant switching scheme for AC power that minimizes failed open circuit and closed circuit conditions, and detection circuitry to detect when a switch has failed. The present invention has particular utility in high-power AC redundant switching systems and will be described in reference to such utility, however the present invention has general utility in redundant switching circuits and systems.
2. Description of Related Art
Redundant power switch circuits are known. For example, U.S. Pat. No. 5,256,905 issued to Streich et al. discloses a controller for controlling one or more AC power loads through switch devices such as triacs. The triacs are gated sequentially within each half cycle such that the peak load on the low voltage control circuitry is equal to the load created by gating only a single triac. Distribution of the gating of the triacs is accomplished through the use of a timing circuit or microprocessor, or RC timing circuits having different time constants. Other redundant topologies can be found in U.S. Pat. Nos. 4,880,994 and 4,244,277.
However, in high voltage applications for example, it is an important design consideration in redundant switch systems to determine if and when a particular switch within the switch array has failed in a stuck closed (i.e., short) condition, since a short condition on any one of the switches can produce unwanted high voltage conditions on other portions of a redundant system. Thus, there is a need to provide a redundant switch array that can couple an available AC power line to a load that includes detection circuitry to determine when a switch within the switch array has stuck closed.
Accordingly, the present invention solves the aforementioned drawbacks of the prior art by providing a redundant switch system including component failure detection circuitry. The switch system includes a redundant switch array to permit continued operation in the event of a failure of one of the switches within the array. The component detection system includes circuitry to indicate that a failure condition exists within the switch array.
In one embodiment, the present invention provides a redundant switch array system, comprising: a plurality of switches formed in a redundant array for coupling an available power line to a load; a switch controller generating a switch control signal for instructing each said switch open or close based on the availability of said power line; and detection circuitry coupled to each said switch for detecting the conduction state of each said switch and generating a detection signal to said controller if said switch is conducting.
In another embodiment, the present invention provides a redundant switch system including component failure detection circuitry, comprising: a plurality of AC power lines; a switch array comprising a plurality of redundant switches for coupling one of said AC power lines to a load; a switch controller generating a switch control signal for instructing each said switch open or close based on the availability of said AC power lines; and detection circuitry coupled to each said switch for detecting the conduction state of each said switch and generating a detection signal to said controller if said switch is conducting.
In system level embodiment, the present invention provides a redundant switch system including component failure detection circuitry, comprising: a plurality of AC power lines; a switch array comprising a plurality of redundant triac switches for coupling one of said AC power lines to a load; a switch controller generating a switch control signal for instructing each said switch open or close based on the availability of said AC power lines; and detection circuitry coupled to each said switch for detecting the conduction state of each said switch and generating a detection signal to said controller if said switch is conducting, and each said detection circuitry coupled in parallel to said triac circuit, said triac switch generating a leakage current across said detection circuitry when said switch is open, said detection circuitry generating a detection signal based upon the absence of said leakage current, wherein said controller receiving said detection signal and comparing said detection signal to said switch control signal to determine if a given one of said switches is stuck in a closed position.
It will be appreciated by those skilled in the art that although the following Detailed Description will proceed with reference being made to preferred embodiments and methods of use, the present invention is not intended to be limited to these preferred embodiments and methods of use. Rather, the present invention is of broad scope and is intended to be limited as only set forth in the accompanying claims.
Other features and advantages of the present invention will become apparent as the following Detailed Description proceeds, and upon reference to the Drawings, wherein like numerals depict like parts, and wherein: